Mounting structure for down-pressure system for opener assembly of agricultural implement

ABSTRACT

A down-pressure system for an agricultural implement has a linear actuator connected between a frame assembly and an opener assembly. A mounting structure for connecting the linear actuator to the opener assembly includes a bushing and an alignment member attached to the linear actuator. The bushing has protrusions extending transversely from opposite sides of a longitudinal axis of the linear actuator. Each protrusion has a curved engagement surface for engaging a flat surface on the opener assembly to prevent bending stresses on the linear actuator when the opener assembly is raised and lowered. The alignment member is arranged to lock the bushing into a predetermined rotational position about a longitudinal axis of the linear actuator relative to the opener assembly. The alignment member comprises a first structure that mates with a corresponding structure on the bushing, and a second structure that engages opposite sides of the opener assembly.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to opener assemblies foragricultural implements, and in particular, to a mounting structure fora down-pressure system for use with opener assemblies of an agriculturalimplement.

Description of the Prior Art

Agricultural seeders used in no-till farming practices require openerswith down-pressure systems that provide a relatively high downforce foradequate ground penetration. An example of such openers is shown in U.S.Pat. No. 4,760,806 issued to Bigbee et al. This type of opener,commercially available on John Deere xx50, xx60, and xx90-series graindrills, has a down-pressure spring that compresses to apply a downforceto the opener.

A seed drill opener assembly 10 having a conventional down-pressuresystem 11 is illustrated in FIG. 1. A rockshaft assembly 12 for raisingand lowering the opener assembly 10 is arranged to pivot about atransverse horizontal axis. The rockshaft assembly 12 is rotatablebetween a first position in which the opener assembly 10 is raised fortransport, and a second position in which the opener assembly 10 islowered for engaging the soil.

The opener assembly 10 is mounted to the rockshaft assembly 12 by anopener arm 13. The opener arm 13 is pivotally connected to a mountingbracket 14 on the rockshaft assembly 12. The down-pressure system 11provides a down-force on the opener assembly 10. The down-pressuresystem 11 includes a mechanical coil spring 15 connected between themounting bracket 14 on the rockshaft assembly 12 and the opener assembly10 (specifically, an extension of opener arm 13). The down-pressuresystem 11 shown in FIG. 1 is similar to the conventional down-pressuresystem disclosed in the '806 patent.

The conventional down-pressure system 11 provides an effective range ofup and down movement of the opener assembly 10 that is less than desiredin typical field conditions. The coil spring 15 compresses about 1 to2.5 inches from being completely relaxed to what is optimal for normalfield operation, depending on the down-pressure deployed (how much twistof the rockshaft hydraulically, and how much frame weight is available).The coil spring 15 can be compressed further if it strikes an obstacleor goes up over a big mound of soil. However, the coil spring 15 startsto relax in the smallest depression (due to the angles involved, an inchof compression or decompression of the coil spring 15 results in about3.5 inches of opener up/down travel at the gauge wheel 16). As a result,the coil spring 15 becomes ineffective soon thereafter and no longersupplies enough downforce to keep the opener at the desired depthsetting. The lack of adequate downforce results in seeds S that are tooshallow or perhaps even on top of the soil surface and can also resultin failure to cut stalks, stubble, and leaves (a.k.a. “residue” ormulch) lying on the soil surface (the so-called hairpinning ofresidue—folding and tucking the residue into the furrow F, instead ofcutting it).

To help alleviate this problem, most drill operators will run moredown-pressure, and add extra ballast to the frame/toolbar. This resultsin some of the openers across the width of the implement having far moredownforce than necessary, in order to keep the majority of openersengaged in the soil. Even so, there are far too many instances whereindividual openers, or groups of openers, will not be cutting thestubble and the soil adequately. For example, if the opener is in asmall depression (including wheel tracks in long-term no-till soilconditions) causing the spring to relax 25%, there will be anapproximately 25% reduction in down-force on that opener, which oftencauses loss of depth consistency, and/or hairpinning. Seeds that are tooshallow or are tucked into straw or stalks will often fail to establish,due to inadequate protection from drying out, or increased diseasepressure, or predation. Plants thus weakened may be subject towinter-kill or winter-injury if the crop is an overwintering crop, suchas winter wheat.

Down-pressure systems that use double-acting hydraulic cylinders toraise and lower opener assemblies are known in the prior art. Forexample, U.S. Pat. No. 5,724,902 issued to Janelle et al. discloses anagricultural seeder that uses a double-acting hydraulic cylinder toapply down-pressure to the opener assembly and to raise the openerassembly into a transport position.

A hydraulic down-pressure system for an implement having openerassemblies 21 mounted to a rockshaft 24 is described in Applicant's U.S.Patent Application No. 62/259,471 filed on Nov. 24, 2015, the content ofwhich is incorporated herein by reference. An opener assembly 21 forthis system is illustrated in FIG. 2 and includes an opener arm 13 and afurrow opener blade 37 (a.k.a. opener “disk”). The opener arm 13 has afirst end 38 pivotally connected to a respective one of the mountingbrackets 14, and a second end 39 supporting the furrow opener blade 37.

A down-pressure system 20 is associated with the opener assembly 21 toprovide an adjustable and constant downforce on the opener blade 37. Thedown-pressure system 20 includes a linear actuator 50 having a first end51 pivotally connected to the mounting bracket 14, and a second end 52connected to the opener assembly 21. The linear actuator 50 is asingle-action hydraulic cylinder with a port 53 connected to a source ofpressurized hydraulic fluid that forces a piston rod of the cylinder 50in an extended direction to apply downforce to the opener assembly 21.The first end 51 of the hydraulic actuator 50 is spaced from the firstend 38 of the opener arm 13 so that changing the length of the hydraulicactuator 50 causes the opener arm 13 to pivot relative to the mountingbracket 14. This arrangement also allows the pressure applied to extendthe hydraulic actuator 50 to be transferred to the opener assembly 21 asa downward biasing force on the opener assembly 21.

However, under some operating conditions, an excessive amount of bendingforce may be imparted to the rod 65 of the hydraulic cylinder 50. Thebending force is caused by the cylinder 50 not being parallel to themain arm 13 of the opener.

There is a need for an improved down-pressure system for use with seeddrill opener assemblies, and particularly a hydraulic down-pressuresystem having a mounting structure that minimizes bending stresses onthe actuator.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improveddown-pressure system for use with seed drills and other agriculturalimplements.

A further object of the present invention is to provide a mountingstructure for a hydraulic down-pressure system that minimizes bendingstresses on the hydraulic actuator.

A further object of the present invention is to provide a down-pressuresystem that can be retrofitted to existing implements in place of OEMmechanical spring down-pressure systems.

A further object of the present invention is to provide a down-pressuresystem for opener assemblies that increases a range of movement of theopener assembly while maintaining a consistent and uniform downforce onthe opener assembly.

To accomplish these and other objects of the invention, a down-pressuresystem for an agricultural implement is provided having a linearactuator connected between a frame assembly and an opener assembly. Amounting structure for connecting the linear actuator to the openerassembly includes a bushing and an alignment member attached to thelinear actuator. The bushing has protrusions extending transversely fromopposite sides of a longitudinal axis of the linear actuator. Eachprotrusion has a curved engagement surface for engaging a flat surfaceon the opener assembly to prevent bending stresses on the linearactuator when the opener assembly is raised and lowered. The alignmentmember is arranged to lock the bushing into a predetermined rotationalposition about a longitudinal axis of the linear actuator relative tothe opener assembly. The alignment member comprises a first structurethat mates with a corresponding structure on the bushing, and a secondstructure that engages opposite sides of the opener arm 13.

According to one aspect of the present invention, an agriculturalimplement is provided, comprising: a frame assembly adapted for forwardmovement over a field; an opener assembly comprising an opener arm and afurrow opener, the opener arm having a first end pivotally connected tothe frame assembly at a first connection point, and a second endsupporting the furrow opener; and a down-pressure system for adjustablybiasing the opener assembly. The down-pressure system comprises a linearactuator having a first actuator end connected to the frame assembly anda second actuator end connected to the opener assembly by a mountingstructure. The mounting structure comprises a bushing attached to thelinear actuator, the bushing having at least one protrusion with acurved engagement surface facing a flat surface on a top side of theopener assembly for engaging the flat surface on the opener assembly toimpart a downforce on the opener assembly without imparting bendingstresses on the linear actuator.

Numerous other objects of the present invention will be apparent tothose skilled in this art from the following description wherein thereis shown and described an embodiment of the present invention, simply byway of illustration of one of the modes best suited to carry out theinvention. As will be realized, the invention is capable of otherdifferent embodiments, and its several details are capable ofmodification in various obvious aspects without departing from theinvention. Accordingly, the drawings and description should be regardedas illustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more clearly appreciated as thedisclosure of the invention is made with reference to the accompanyingdrawings. In the drawings:

FIG. 1 is a side view of a prior art seed drill opener assembly mountedto an adjustable rockshaft with a mechanical spring for applyingdownforce.

FIG. 2 is a side view of a seed drill opener assembly with asingle-action hydraulic cylinder connected between an adjustablerockshaft and the opener assembly, as described in Applicant's copendingapplication.

FIG. 3 is a side view of a seed drill opener assembly with a hydraulicdown-pressure system and a mounting structure that minimizes bendingstresses on the hydraulic actuator.

FIGS. 4 and 5 are side views of the implement frame showing therockshaft, opener arm, and hydraulic down-pressure system with theopener arm illustrated in a lowered position (FIG. 4) and a raisedposition (FIG. 5).

FIG. 6 is an exploded perspective view of a mounting structure for oneof the single-action hydraulic cylinders used in the down-pressuresystem of the present invention.

FIGS. 7 to 10 are perspective, top, side and end views, respectively, ofa bushing used in the mounting structure of the present invention.

FIG. 11 is a side view of a bushing according to another embodiment foruse in the mounting structure of the present invention.

FIGS. 12 to 14 are perspective, top and side views, respectively, of aflange used in the mounting structure of the present invention.

FIG. 15 is a perspective view of the bushing and flange of the mountingstructure assembled together.

DETAILED DESCRIPTION OF THE INVENTION

A mounting structure 70 for a down-pressure system 20 of an agriculturalimplement with opener assemblies 21 according to the present inventionwill now be described in detail with reference to FIGS. 3 to 15 of theaccompanying drawings.

The agricultural implement includes a frame assembly adapted for forwardmovement over a field. A hitch structure (not shown) is provided at thefront of the frame assembly, and a plurality of transport wheels (notshown) are provided to support the frame assembly above the ground.

The frame assembly includes a rockshaft assembly 12, also sometimesreferred to as a “torque tube,” which is arranged to pivot about atransverse horizontal axis. The rockshaft assembly 12 may be in the formof a heavy square metal tube 24, as shown in cross section in FIG. 3. Adouble-acting hydraulic cylinder (not shown) is used to rotate therockshaft assembly 12 between a first position (FIG. 5) in which openerassemblies 21 are raised for transport, and a second position (FIG. 4)in which the opener assemblies 21 are lowered for engaging the soil.

The implement includes a plurality of opener assemblies 21 arranged inspaced relationship across the width of the implement. The openerassemblies 21 are mounted to respective mounting brackets 14 attached tothe rockshaft 12. The mounting brackets 14 are each attached to the tube24 of the rockshaft 12 using four threaded fasteners 34 and a clampingstructure 35.

Each of the opener assemblies 21 includes an opener arm 13 and a furrowopener blade 37 (a.k.a. opener “disk”). The opener arm 13 has a firstend 38 pivotally connected to a respective one of the mounting brackets14 on the rockshaft tube 24, and a second end 39 supporting a hub 40 onwhich the furrow opener blade 37 is mounted. The opener blade 37 isarranged to operate at a slight angle to the direction of travel to cuta furrow F in the soil as the implement moves through the field.Alternatively, a pair of blades 37 may be arranged to create furrow F. Agauge wheel 16 is supported for rotation adjacent to the opener blade 37to limit the blade 37 to a desired depth of operation. An adjustmentmechanism 42 is provided for adjusting the gauge wheel 16 verticallywith respect to the opener blade 37 to change the depth of operation.

A firming wheel 43 follows behind the opener blade 37 for firming theseeds S into soil in the bottom of the furrow F created by the openerblade 37 to provide good seed-to-soil contact in the furrow F. A firmingadjustment mechanism 44 allows the downforce on the firming wheel 43 tobe adjusted.

A closing wheel 45 follows behind the firming wheel 43 for crushing theside of the furrow F to provide a layer of soil over the seeds Sdeposited in the furrow F. A closing adjustment mechanism 46 allows thedownforce on the closing wheel 45 to be adjusted.

A seed tube 47 and seed boot 48 are provided for directing seeds Sdownwardly and rearwardly into the furrow F created by the opener blade37. A seed bounce flap 49 is attached to trail below and/or behind theseed boot 48 for preventing seeds S from bouncing out of the furrow F asthey are being deposited.

A down-pressure system 20 is associated with each of the openerassemblies 21 to provide an adjustable and uniform downforce on theopener blade 37. The down-pressure system 20 includes a linear actuator50 having a first end 51 pivotally connected to a respective one of themounting brackets 14 on the rockshaft tube 24, and a second end 52connected to the opener assembly 21.

In the illustrated embodiment, the linear actuator 50 is a single-actionhydraulic cylinder. The single-action cylinder 50 has a port 53connected to a source of pressurized hydraulic fluid that forces thesingle-action hydraulic cylinder 50 in an extended direction to applydownforce to the opener assembly 21. In an alternative embodiment, thelinear actuator 50 can be a double-acting hydraulic cylinder.

The first end 51 of the hydraulic actuator 50 is spaced from the firstend 38 of the opener arm 13 so that changing the length of the hydraulicactuator 50 causes the opener arm 13 to pivot relative to the mountingbracket 14. This arrangement also allows the pressure applied to extendthe hydraulic actuator 50 to be transferred to the opener assembly 21 asa downward biasing force on the opener assembly 21.

The down-pressure system 20 of the present invention has been describedabove as being used in an agricultural seeding drill. However, thedown-pressure system 20 may also be used with other implements havingopener assemblies, such as fertilizer applicators and the like.

As explained above, an embodiment of the present invention usessingle-action cylinders 50 as down-pressure systems 20 on the individualopener assemblies 21. A suitable single-action cylinder 50 for thispurpose is described in Applicant's Application No. 62/259,471 filed onNov. 24, 2015. The single-action cylinder has pin openings 64 formed atthe first end 51 of the cylindrical housing 63 (FIG. 6) for connectingto the mounting bracket 14 (FIGS. 2-5). A plunger rod 65 protrudes fromthe second end 66 of the cylindrical housing 63 for connecting to theopener assembly 21.

The plunger rod 65 of the linear actuator 50 has a second actuator endconnected to the opener assembly 21 by the mounting structure 70 (FIG.4). The mounting structure 70 includes a bushing 71 and an alignmentmember 72 attached to the plunger rod 65. The plunger rod 65 includes athreaded end portion 67, a cylindrical shaft portion 68, and a shoulder69 between the threaded end portion 67 and the cylindrical shaft portion68. The plunger rod 65 extends through a longitudinal bore 73 of thebushing 71 until the shoulder 69 of the plunger rod 65 engages acorresponding annular surface 74 within the bushing 71. The threaded endportion 67 of the plunger rod 65 extends out of the bottom side 75 ofthe bushing 71. The bushing 71 is secured to the rod 65 by means of apress-fit, sometimes reinforced with adhesive compount.

A first threaded nut 76 (FIG. 6) mates with the threaded end portion 67of the plunger rod 65 to secure the mounting structure 70. A second nut77 can be used as a locking jam nut to lock the first threaded nut 76against rotation on the threaded end portion 67. The alignment member 72is sandwiched between the bottom side 75 of the bushing 71 and the firstthreaded nut 76 to connect the threaded actuator end 67 to the openerassembly 21.

The mounting structure 70 is assembled onto the opener assembly 21 byplacing the bushing 71 into a mounting hole 78 (FIG. 3) in the openerassembly 21 from a top side of the mounting hole 78 until a bottom side75 of the bushing 71 extends from the bottom of the mounting hole. Thebushing 71 fits loosely in the mounting hole 78 in the opener assembly21 so that it can rock within the mounting hole 78 as the openerassembly 21 moves between its raised and lowered positions.

The bushing 71 has a pair of protrusions 79 extending transversely fromopposite sides of a longitudinal axis of the linear actuator 50. Theprotrusions 79 each have a respective curved engagement surface 80 forengaging a flat surface 81 on the opener assembly 21. The flat surface81 is located on a top side of the opener assembly 21 and can be a flatwasher, as shown in FIGS. 3 to 6. The flat washer 81 is sandwichedbetween the curved engagement surfaces 80 of the bushing 71 and the topside of the mounting hole 78 in the opener assembly 21. The curvedengagement surfaces 80 of the bushing are convex in a direction facingthe flat surface 81 on the opener assembly 21.

The curved engagement surfaces 80 in the illustrated embodiment in FIGS.3 to 10 are horizontal cylindrical segments. The horizontal cylindricalsegments are each shaped to correspond with a horizontal cylindricalsegment cut from a cylinder having an axis of symmetry parallel with anaxis of rotation of the opener arm 13 at its pivotal connection 38 tothe frame assembly 12.

The first end 38 of the opener arm 13 is pivotally connected to theframe assembly 12 for rotation about a first transverse axis, and thefirst actuator end 51 of the linear actuator 50 is pivotally connectedto the frame assembly for rotation about a second transverse axis 64spaced from the first transverse axis. The curved engagement surfaces 80on the bushing 71 comprise horizontal cylindrical segments having anaxis of symmetry parallel with the first and second transverse axes ofthe opener arm 13 and linear actuator 50, respectively. The curvedengagement surfaces 80 lie in an arc about a third transverse axislocated above the curved engagement surfaces 80. The third transverseaxis intersects a longitudinal axis of the linear actuator 50 betweenthe bushing 71 and the first actuator end 51.

The alignment member 72 is placed in mating engagement with the bottomside 75 of the bushing 71 on the bottom side of the mounting hole 78 inthe opener assembly 21. The bushing 71 has a pair of integral lugs 82extending from its bottom side 75. The alignment member 72 comprises aplate with a bore 83 for receiving the threaded end 67 of the plungerrod 65, and a pair of cutouts 84 for receiving the lugs 82 on the bottomside of the bushing 71. The lugs 82 of the bushing 71 are mated with thecutouts 84 in the alignment member 72 so that the bushing 71 is held ina fixed rotational position relative to the alignment member 72.

The alignment member 72 has a second structure comprising a pair of arms85 that extend from the plate and are arranged to engage opposite sidesof the opener arm 13. The alignment member 72 is arranged to lock thebushing 71 into a predetermined rotational position about a longitudinalaxis of the linear actuator 50 relative to the opener assembly 21. Thepredetermined angular position is a position in which the protrusions 79extend transverse to a direction of travel of the implement.

The curved engagement surfaces 80 on the bushing 71 allow a downforce tobe imparted by the linear actuator 50 through the bushing 71 to the flatsurface 81 on the opener assembly 21 without imparting bending stresseson the linear actuator 50. As the opener arm 13 is moved between itslowered position (FIG. 4) and its raised position (FIG. 5), the curvedsurface 80 of the bushing 71 will roll across the flat surface 81 on theopener assembly 21 to impart a downforce to the opener assembly 21. Thecurved surface 80 of the bushing 71 functions to eliminate or minimizeany bending stresses on the linear actuator 50 when a downforce isapplied to the opener assembly 21.

A bushing 90 according to another embodiment of the present invention isillustrated in FIG. 11. The bushing 90 has a pair of protrusions 91extending transversely from opposite sides of the longitudinal axis ofthe bushing 90. The protrusions 91 each have a respective curvedengagement surface 92 for engaging a flat surface 81 on the openerassembly 21. The curved engagement surface 92 has a smaller radius thanthe curved surface 80 of the bushing 71 illustrated in FIG. 9. Thesmaller radius curved surface 92 functions to minimize bending stresseson the linear actuator 50, similar to the curved surface 80 of thebushing 71 described above, but more effectively. The smaller radiuscurved surface 92 also has the advantage of keeping the longitudinalforces transferred from the bushing 90 to the opener assembly 21 morecentered with the longitudinal axis of the linear actuator 50 as theopener assembly 21 is moved between its lowered and raised positions.The radius is ideally quite small (0.1 inch), within the constraints ofmaterials used for bushing 71 and durability of flat surface 81.

While the invention has been specifically described in connection withspecific embodiments thereof, it is to be understood that this is by wayof illustration and not of limitation, and the scope of the appendedclaims should be construed as broadly as the prior art will permit.

What is claimed is:
 1. An agricultural implement, comprising: a frameassembly adapted for forward movement over a field; an opener assemblycomprising an opener arm and a furrow opener, said opener arm having afirst end pivotally connected to said frame assembly at a firstconnection point, and a second end supporting said furrow opener; adown-pressure system for adjustably biasing the opener assembly, saiddown-pressure system comprising a linear actuator, said linear actuatorhaving a first actuator end connected to said frame assembly at a secondconnection point; and said linear actuator has a second actuator endconnected to said opener assembly by a mounting structure, said mountingstructure comprises a bushing attached to said linear actuator, saidbushing having at least one protrusion with a curved engagement surfacefacing a flat surface on a top side of said opener assembly for engagingthe flat surface on said opener assembly to impart a downforce on saidopener assembly without imparting bending stresses on said linearactuator.
 2. The agricultural implement according to claim 1, whereinsaid at least one protrusion comprises a pair of protrusions extendingtransversely from opposite sides of a longitudinal axis of said linearactuator, each protrusion comprising a respective curved engagementsurface for engaging a flat surface on said opener assembly.
 3. Theagricultural implement according to claim 2, wherein each of said curvedengagement surfaces comprises a horizontal cylindrical segment.
 4. Theagricultural implement according to claim 1, wherein said curvedengagement surface comprises a horizontal cylindrical segment.
 5. Theagricultural implement according to claim 1, wherein said curvedengagement surface is shaped to correspond with a horizontal cylindricalsegment cut from a cylinder having an axis of symmetry parallel with anaxis of rotation of the opener arm at its pivotal connection to saidframe assembly.
 6. The agricultural implement according to claim 1,wherein said first end of said opener arm is pivotally connected to saidframe assembly for rotation about a first transverse axis, said firstactuator end of said linear actuator is pivotally connected to saidframe assembly for rotation about a second transverse axis spaced fromsaid first transverse axis, and said curved engagement surface comprisesa horizontal cylindrical segment having an axis of symmetry parallelwith said first and second transverse axes.
 7. The agriculturalimplement according to claim 1, wherein said curved engagement surfaceis convex in a direction facing the flat surface on said openerassembly.
 8. The agricultural implement according to claim 1, whereinsaid curved engagement surface lies in an arc about a transverse axislocated above said lower end of said bushing.
 9. The agriculturalimplement according to claim 1, wherein said first end of said openerarm is pivotally connected to said frame assembly for rotation about afirst transverse axis, said first actuator end of said linear actuatoris pivotally connected to said frame assembly for rotation about asecond transverse axis spaced from said first transverse axis, and saidcurved engagement surface lies in an arc about a third transverse axisparallel with said first and second transverse axes.
 10. Theagricultural implement according to claim 9, wherein said thirdtransverse axis intersects a longitudinal axis of said linear actuator.11. The agricultural implement according to claim 1, wherein said flatsurface on said opener assembly is a flat washer.
 12. The agriculturalimplement according to claim 1, wherein said mounting structure furthercomprises an alignment member arranged to lock said bushing into apredetermined rotational position about a longitudinal axis of saidlinear actuator relative to said opener assembly.
 13. The agriculturalimplement according to claim 12, wherein said alignment member comprisesa first structure that mates with a corresponding structure on saidbushing, and a second structure that engages the opener arm.
 14. Theagricultural implement according to claim 12, wherein said at least oneprotrusion comprises a pair of protrusions extending transversely fromopposite sides of a longitudinal axis of said linear actuator, and saidpredetermined rotational position of said bushing is a position in whichsaid protrusions extend transverse to a direction of travel of theimplement.
 15. The agricultural implement according to claim 12, whereinsaid bushing has a bottom side with a pair of integral lugs, and whereinsaid alignment member comprises a plate with a bore and a pair ofcutouts for receiving said lugs on the bottom side of the bushing, and apair of arms that extend from the plate and are arranged to engageopposite sides of the opener arm.
 16. The agricultural implementaccording to claim 12, wherein said second actuator end of said linearactuator comprises a threaded rod that extends through a longitudinalbore of said bushing, a mounting hole in said opener assembly, and thebore in said alignment member, and wherein said alignment member issandwiched between the bushing and a threaded nut that mates with saidthreaded rod to connect said second actuator end to said openerassembly.
 17. The agricultural implement according to claim 1, whereinsaid frame assembly includes a rockshaft assembly arranged to pivotabout a transverse horizontal axis, and said first end of said openerarm is pivotally connected to said rockshaft assembly at said firstconnection point, and said first actuator end of said linear actuator isconnected to said rockshaft assembly at said second connection point.18. In an agricultural implement having a frame assembly adapted forforward movement over a field, and an opener assembly having an openerarm with a first end pivotally connected at a first connection point tosaid frame assembly and a second end supporting a furrow opener, anadjustable down-pressure system for rotatably biasing the opener arm,the down-pressure system comprising: a hydraulic linear actuator havinga first actuator end connected to said frame assembly at a secondconnection point spaced from said first connection point, and a secondactuator end placed in a mounting hole of said opener assembly andconnected to said opener assembly by a mounting structure, said mountingstructure comprising a bushing attached to said linear actuator, saidbushing having at least one protrusion with a curved engagement surfacefacing a flat surface on a top side of said opener assembly for engagingthe flat surface on said opener assembly to impart a downforce on saidopener assembly without imparting bending stresses on said linearactuator.
 19. In an agricultural seed drill having a frame assemblyadapted for forward movement over a field, an opener assembly having anopener arm and a furrow opener, said opener arm having a first endpivotally connected to the frame assembly and a second end supportingthe furrow opener, and a down-pressure system for adjustably biasing theopener arm, the down-pressure system comprising: a hydraulic linearactuator having a first actuator end connected to said frame assembly ata second connection point spaced from said first connection point, and asecond actuator end placed in a mounting hole of said opener assemblyand connected to said opener assembly by a mounting structure, saidmounting structure comprising a bushing attached to said linearactuator, said bushing having at least one protrusion with a curvedengagement surface facing a flat surface on a top side of said openerassembly for engaging the flat surface on said opener assembly to imparta downforce on said opener assembly without imparting bending stresseson said linear actuator.